One of the solutions employed because of its direct character consists of using a programmable frequency divider on the frequency given by a signal generator, this divider being able to be directly controlled by a sequencer or a calculator. This type of solution, while it permits the effective obtaining of frequency variation laws corresponding to those pre-established by the program, has however the inherent inconvenience to systems controlled by program, which, most often, do not permit processing in real time, the calculation times of the programs, as a function of the desired applications, can become very significant for obtaining a response of the system and a corresponding frequency variation in real time. Further, the highly discrete character of the number of values of division ratios able to be used in the programmable divider used permits establishment of only certain predetermined frequency variation laws, laws corresponding to discrete variations of frequency, any continuous variation between the mentioned discrete values being excluded with as a result a corresponding absence of continuous variation between elementary frequency values constituting a programmed law.